A filtering device may be seen by reference to Japanese Patent No. 57,075,113. In the filtering device disclosed therein and in other publications making up the state of the art, the goal of such filtering devices is to avoid impediments to the effectiveness of filtration occurring during the filtration process, and in particular in the ultra-filtration process. Such impediments include the formation of filter cakes, the plugging of filter pores, the formation of gel and salt polarizations, and lowering of the filtering capacity caused by the foregoing impediments. A reduced lowering of the filtering capacity is achieved by employment of high flow rates of the filtered material in directions perpendicular to the filtration direction, which directional employment avoids or at least strongly reduces the formation of layers lowering the filtering capacity. Such a directional employment process is commonly known as "c r 055 flow" filtration.
The known prior art in this regard exhibits a variety of disadvantages. In U.S. Pat. No. 3,702,659 (Swiss Patent No. 625,712) a fluid is filtered by allowing it to flow tangentially against a round filter plate. The velocity of the fluid either increases from the outside to the inside or decreases from the inside to the outside due to the continuity conditions. If the filter plate has enclosed channels through which the fluid flows, the average flow velocity is constant. However, a high flow resistance occurs in the narrow channels. The result of such high flow resistance is a turbulent flow of the fluid. The turbulent flow of the fluid causes high shear forces to occur, resulting in a considerable increase in expended energy. Negative effects on the mixture being filtered can result, particularly when the liquids to be filtered contain either unstable, large molecules or plant or animal cells. Chemical changes in the materials being filtered may even occur. Furthermore, such prior art device is only suitable for one particular filter type which is produced by the manufacturer of the prior art device. Alternatively, other types of filters can be used with such device but only by employing retentive areas and/or complicated perforations within the filter plate.
Most of the known filter devices are installed in their own specialized container. This results in considerable expense in the installation of new filter plates in such specialized containers and in the construction of such specialized containers which can withstand the high pressures necessary for ultrafiltration. Sterilization of such specialized containers can be difficult, due in some instances to the specialized configurations thereof, for example, narrow filtration channels in the container.
It is an object of the present invention to provide a filtering device which overcomes all the above-described disadvantages of the prior art devices and which is easy to handle and can be manufactured at a favorable cost.